Method for producing single crystal silicon solar cell and single crystal silicon solar cell

ABSTRACT

There is disclosed a method for producing a single crystal silicon solar cell comprising the steps of: implanting hydrogen ions or rare gas ions into a single crystal silicon substrate through an ion implanting surface thereof to form an ion implanted layer in the single crystal silicon substrate; closely contacting the single crystal silicon substrate and a transparent insulator substrate with each other via a transparent adhesive while using the ion implanting surface as a bonding surface; curing the transparent adhesive; applying an impact to the ion implanted layer to mechanically delaminate the single crystal silicon substrate thereat to leave a single crystal silicon layer; forming a plurality of diffusion regions having a second conductivity type at the delaminated surface side of the single crystal silicon layer, in a manner that a plurality of first conductivity-type regions and a plurality of second conductivity-type regions are present at the delaminated surface of the single crystal silicon layer; forming pluralities of individual electrodes on the pluralities of first and second conductivity-type regions of the single crystal silicon layer, respectively; and forming collector electrodes for the individual electrodes, respectively. There can be provided a single crystal silicon solar cell as a see-through type solar cell, including a thin-film light conversion layer made of single crystal silicon having a higher crystallinity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing a single crystalsilicon solar cell and to a single crystal silicon solar cell, andparticularly to a method for producing a single crystal silicon solarcell comprising a step of forming a single crystal silicon layer on atransparent insulator substrate and to a single crystal silicon solarcell having a single crystal silicon layer on a transparent insulatorsubstrate.

2. Description of the Related Art

Solar cells comprising silicon as main materials are classified intosingle crystal silicon solar cells, polycrystalline silicon solar cells,and amorphous silicon solar cells, based on crystallinities thereof.Among them, single crystal silicon solar cells are each provided assolar cell elements by cutting a single crystal ingot prepared by acrystal pulling method by a wire saw into a wafer shape slice, workingthe slice into a wafer having a thickness of 100 to 200 μm, and formingp-n junctions, electrodes, a protective film, and the like thereon.

In case of polycrystalline silicon solar cells, there is fabricated apolycrystalline ingot by crystallizing a molten metal silicon in a moldwithout relying on crystal pulling, and the ingot is cut into a wafershape slice by a wire saw in the same manner as single crystal siliconsolar cells, and the slice is worked into a wafer having a thickness of100 to 200 μm, and formed with p-n junctions, electrodes, a protectivefilm, and the like thereon, to provide solar cell elements, in the samemanner as a single crystal silicon substrate.

In case of amorphous silicon solar cells, there is formed an amorphoussilicon hydride film on a substrate by decomposing a silane gas bydischarge in a vapor phase such as by a plasma CVD method, and diborane,phosphine, and the like as doping gases are added thereto, followed bysimultaneous deposition thereof to simultaneously achieve a p-n junctionformation process and a film-formation process, and followed byformation of electrodes and a protective film, thereby providing solarcell elements. In an amorphous silicon solar cell, since amorphoussilicon as a direct transition type absorbs incident light, theamorphous silicon has a light absorption coefficient which is about oneorder higher than those of single crystal silicon and polycrystallinesilicon (“Solar photovoltaic power generation”, p. 233, by KiyoshiTakahashi, Yoshihiro Hamakawa, and Akio Ushirokawa, Morikita Shuppan,1980), thereby providing an advantage that a thickness of about 1 μm ofan amorphous silicon layer will do which is about a hundredth of that ofa crystal-based solar cell. Thus, expectation is significant foramorphous silicon solar cells capable of effectively utilizingresources, in view of the fact that the annual production volume ofsolar cells has recently exceeded 1 giga-watts in the world and theproduction volume will be further increased.

However, it is inappropriate to determine the effective utilizationratio of resources based on simple comparison with a film thicknessrequired by a crystal-based solar cell, because of exemplarycircumstances that high purity gas materials such as silane and disilaneare used as starting materials for fabrication of amorphous siliconsolar cells, and that the effective utilization ratio of the gasmaterials includes deposition thereof at locations in a plasma CVDapparatus other than at a substrate. Further, an amorphous silicon solarcell has a conversion efficiency of about 10° whereas a crystal-basedsolar cell has a conversion efficiency of about 15%, and there is stillleft a problem of degradation of output characteristic in an amorphoussilicon solar cell under light irradiation.

As such, there have been conducted various approaches for developingthin-film solar cells by utilizing silicon crystal-based materials(“Solar photovoltaic power generation”, p. 217, by Kiyoshi Takahashi,Yoshihiro Hamakawa, and Akio Ushirokawa, Morikita Shuppan, 1980). Forexample, there is deposited a polycrystalline thin-film on an aluminasubstrate, graphite substrate, or the like, by using a trichlorosilanegas, a tetrachlorosilane gas, or the like. The thus deposited film has alot of crystal defects, and the conversion efficiency is low as it is.Thus, it is required to conduct zone melting to improve crystallinity,so as to increase the conversion efficiency (see JP-A-2004-342909, forexample). However, even by conducting such a zone melting method, therehas been still left an exemplary problem that photocurrent responsecharacteristics in a longer wavelength range are lowered because crystalgrain boundaries cause a leak current in a crystal grain boundary andshorten lifetimes of carriers.

SUMMARY OF THE INVENTION

The present invention has been carried out in view of the above problem,and it is therefore an object of the present invention to provide asingle crystal silicon solar cell and a production method thereof, whichsingle crystal silicon solar cell acts as a silicon solar cell where alight conversion layer is provided as a thin-film for effectiveutilization of silicon as a starting material of the silicon solar cell,which single crystal silicon solar cell is excellent in conversioncharacteristics and is less in degradation due to light irradiation, andwhich single crystal silicon solar cell is provided as a see-throughtype solar cell that is usable as a natural lighting window material ofa house or the like and that transmits part of received visible lighttherethrough.

To achieve the above object, the present invention provides a method forproducing a single crystal silicon solar cell, the solar cell includinga transparent insulator substrate and a single crystal silicon layerarranged on the transparent insulator substrate and acting as a lightconversion layer, the method comprising at least the steps of:

preparing the transparent insulator substrate and a single crystalsilicon substrate having a first conductivity type;

implanting at least one of hydrogen ions and rare gas ions into thesingle crystal silicon substrate through an ion implanting surfacethereof to form an ion implanted layer in the single crystal siliconsubstrate;

closely contacting the single crystal silicon substrate and thetransparent insulator substrate with each other via a transparentadhesive while using the ion implanting surface as a bonding surface;

curing and maturing the transparent adhesive into a transparent adhesivelayer, to bond the single crystal silicon substrate and the transparentinsulator substrate to each other;

applying an impact to the ion implanted layer to mechanically delaminatethe single crystal silicon substrate thereat to leave a single crystalsilicon layer;

forming a plurality of diffusion regions having a second conductivitytype at the delaminated surface side of the single crystal siliconlayer, which conductivity type is different from the first conductivitytype, in a manner that a plurality of p-n junctions are formed at leastin the plane direction, and that the plurality of firstconductivity-type regions and the plurality of second conductivity-typeregions are present at the delaminated surface of the single crystalsilicon layer;

forming a plurality of first individual electrodes on the plurality offirst conductivity-type regions of the single crystal silicon layer,respectively, and a plurality of second individual electrodes on theplurality of second conductivity-type regions, respectively; and

forming a first collector electrode for connecting the plurality offirst individual electrodes to one another and a second collectorelectrode for connecting the plurality of second individual electrodesto one another.

By virtue of the method for producing a single crystal silicon solarcell including such steps, it is possible to produce a single crystalsilicon solar cell including a single crystal silicon layer as a lightconversion layer arranged on a transparent insulator substrate.

Since the single crystal silicon substrate and the transparent insulatorsubstrate are bonded to each other by means of the transparent adhesive,both substrates can be strongly bonded to each other. This results in asufficiently strong joining, without applying a high-temperature heattreatment for increasing a bonding force. Further, since the joiningsurfaces are strongly joined to each other in this way, it becomespossible to subsequently apply an impact to the ion implanted layer tothereby mechanically delaminate the single crystal silicon substratethereat, thereby forming a thin single crystal silicon layer on thetransparent insulator substrate. Thus, the single crystal siliconthin-film can be obtained, even without conducting a heat treatment fordelamination.

According to the method for producing a single crystal silicon solarcell including such steps, the formation of the single crystal siliconlayer acting as the light conversion layer is achieved by thedelamination from the single crystal silicon substrate, thereby enablingan enhanced crystallinity of the single crystal silicon layer. Thisresultingly enables an enhanced conversion efficiency of the solar cell.

Further, the delamination of the single crystal silicon substrate forformation of the single crystal silicon layer is conducted as mechanicaldelamination without relying on heating, thereby enabling suppression ofintroduction of cracks, defects, and the like into the light conversionlayer due to a difference of thermal expansion coefficient.

Moreover, the solar cell is made to be a thin-film solar cell having thethin layer of silicon, thereby enabling a silicon material to be savedand effectively utilized.

In turn, the electrodes for extraction of electric power are formed ononly one side of the light conversion layer, thereby enabling provisionof a single crystal silicon solar cell capable of facilitatingextraction of electric power.

In this case, the transparent insulator substrate may be made of any oneof quartz glass, crystallized glass, borosilicate glass, and soda-limeglass.

In this way, the transparent insulator substrate is made of any one ofquartz glass, crystallized glass, borosilicate glass, and soda-limeglass which are transparent insulator substrates having excellentoptical characteristics, thereby enabling a see-through type singlecrystal silicon solar cell to be readily produced. It becomes furtherpossible to readily substitute the thus produced single crystal siliconsolar cell for an existing window glass or the like.

Further, the transparent adhesive is desirably configured to contain atleast one of a silicone resin, an acrylic resin, an alicyclic acrylicresin, a liquid crystal polymer, a polycarbonate, and a polyethyleneterephthalate.

In this way, the transparent adhesive is configured to contain at leastone of a silicone resin, an acrylic resin, an alicyclic acrylic resin, aliquid crystal polymer, a polycarbonate, and a polyethyleneterephthalate, thereby enabling an excellent transparent adhesive layerto be formed because these substances each have a function as anadhesive and have an excellent visible light transmissivity.

Furthermore, the ion implantation is preferably conducted at a depthbetween 0.1 μm inclusive and 5 μm inclusive from the ion implantingsurface.

In this way, the ion implantation is conducted at a depth between 0.1μm-inclusive and 5 μm inclusive from the ion implanting surface, therebyenabling achievement of a thickness between 0.1 μm inclusive and 5 μminclusive for the single crystal silicon layer as the light conversionlayer of the single crystal silicon solar cell to be produced. Thesingle crystal silicon solar cell having the single crystal siliconlayer of such a thickness is allowed to obtain a practical efficiency asa thin-film single crystal silicon solar cell and to save an amount ofsilicon material to be used. Further, the single crystal silicon solarcell having the single crystal silicon layer of such a thickness iscapable of assuredly transmitting part of visible light therethrough.

The present invention further provides a single crystal silicon solarcell produced by any one of the above-mentioned methods for producing asingle crystal silicon solar cell.

In this way, in the single crystal silicon solar cell produced by anyone of the methods for producing a single crystal silicon solar cell,the formation of the single crystal silicon layer acting as the lightconversion layer is achieved by the delamination from the single crystalsilicon substrate, and the delamination of the single crystal siliconlayer is conducted by mechanical delamination without relying onheating, thereby enabling provision of a single crystal silicon layerhaving an enhanced crystallinity. This allows the solar cell to be athin-film solar cell having a higher conversion efficiency as comparedto the film thickness. Further, the thin-film solar cell including thethin single crystal silicon layer allows for effective utilization of asilicon material.

The present invention further provides a single crystal silicon solarcell comprising:

at least, a transparent insulator substrate, a transparent adhesivelayer, and a single crystal silicon layer, which are successivelylaminated;

a plurality of first conductivity-type regions and a plurality of secondconductivity-type regions formed in the single crystal silicon layer ata surface side thereof opposite to the transparent adhesive layer side;

a plurality of p-n junctions formed at least in the plane direction ofthe single crystal silicon layer;

a plurality of first individual electrodes formed on the plurality offirst conductivity-type regions of the single crystal silicon layer,respectively, and a plurality of second individual electrodes formed onthe plurality of second conductivity-type regions of the single crystalsilicon layer, respectively; and

a first collector electrode for connecting the plurality of firstindividual electrodes to one another, and a second collector electrodefor connecting the plurality of second individual electrodes to oneanother.

In this way, the single crystal silicon solar cell comprising:

at least, a transparent insulator substrate, a transparent adhesivelayer, and a single crystal silicon layer, which are successivelylaminated;

a plurality of first conductivity-type regions and a plurality of secondconductivity-type regions formed in the single crystal silicon layer ata surface side thereof opposite to the transparent adhesive layer side;

a plurality of p-n junctions formed at least in the plane direction ofthe single crystal silicon layer;

a plurality of first individual electrodes formed on the plurality offirst conductivity-type regions of the single crystal silicon layer,respectively, and a plurality of second individual electrodes formed onthe plurality of second conductivity-type regions of the single crystalsilicon layer, respectively; and

a first collector electrode for connecting the plurality of firstindividual electrodes to one another, and a second collector electrodefor connecting the plurality of second individual electrodes to oneanother;

acts as a silicon solar cell including a light conversion layer arrangedon a transparent insulator substrate in which the light conversion layeris made of a single crystal silicon layer, thereby allowing the solarcell to have a higher conversion efficiency as compared to the filmthickness of the light conversion layer. Further, the electrodes forextraction of electric power are formed on only one side of the lightconversion layer, thereby facilitating extraction of electric power.

In this case, the transparent insulator substrate is preferably made ofany one of quartz glass, crystallized glass, borosilicate glass, andsoda-lime glass.

In this way, the transparent insulator substrate is made of any one ofquartz glass, crystallized glass, borosilicate glass, and soda-limeglass, thereby enabling a provision of a see-through type single crystalsilicon solar cell having a superior transparency because these glassesare transparent insulator substrates excellent in opticalcharacteristics. It is also easy to substitute the thus produced singlecrystal silicon solar cell for an existing window glass or the like.

Further, the transparent adhesive is preferably configured to contain atleast one of a silicone resin, an acrylic resin, an alicyclic acrylicresin, a liquid crystal polymer, a polycarbonate, and a polyethyleneterephthalate.

In this way, the transparent adhesive layer is configured to contain atleast one of a silicone resin, an acrylic resin, an alicyclic acrylicresin, a liquid crystal polymer, a polycarbonate, and a polyethyleneterephthalate, so that the transparent adhesive layer is excellentlyestablished because these substances each have an excellent visiblelight transmissivity.

Furthermore, the single crystal silicon layer desirably has a thicknessbetween 0.1 μm inclusive and 5 μm inclusive.

In this way, the single crystal silicon layer having a thickness between0.1 μm inclusive and 5 μm inclusive allows to obtain a practicalefficiency as a thin-film single crystal silicon solar cell and to savean amount of silicon material to be used. Further, the single crystalsilicon solar cell having the single crystal silicon layer of such athickness is capable of assuredly transmitting part of visible lighttherethrough.

Moreover, the single crystal silicon solar cells can each be desirablyseen through from one surface side toward the other surface side.

In this way, the single crystal silicon solar cell can be seen throughfrom one surface side toward the other surface side, so that the solarcell can be applied to various situations such that the solar cell canbe substituted for an existing window glass or the like.

According to the method for producing a single crystal silicon solarcell of the present invention, it is possible to produce a see-throughtype thin-film solar cell which is excellent in crystallinity and has asingle crystal silicon layer having a higher conversion efficiency as alight conversion layer. Further, electrodes for extracting an electricpower are formed on only one surface side of the light conversion layer,thereby enabling establishment of a single crystal silicon solar cellcapable of easy extraction of electric power.

Moreover, the single crystal silicon solar cell according to the presentinvention acts as a silicon solar cell including a light conversionlayer arranged on a transparent insulator substrate in which the lightconversion layer is made of a single crystal silicon layer, therebyallowing the solar cell to have a higher conversion efficiency ascompared to the film thickness of the light conversion layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process diagram of an example of a method for producing asingle crystal silicon solar cell according to the present invention;and

FIG. 2 is a schematic cross-sectional view of an example of a singlecrystal silicon solar cell according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, there has been demanded a higher conversionefficiency even in a thin-film solar cell capable of saving a siliconmaterial, and as such, it has been demanded to further improvecrystallinity in addition to adoption of a crystal-based solar cell.

Under such circumstances, the present inventors have found out thatcrystallinity of a silicon layer as a light conversion layer can beenhanced by obtaining a single crystal silicon thin-film from a singlecrystal silicon substrate after once bonding the single crystal siliconsubstrate and a transparent insulator substrate to each other. Further,the present inventors have conceived that crystallinity of the singlecrystal silicon layer can be satisfactorily maintained, by adopting andcuring a transparent adhesive upon bonding the single crystal siliconsubstrate and the transparent insulator substrate to each other tothereby increase a bonding strength therebetween without ahigh-temperature heat treatment, and by conducting mechanicaldelamination upon delaminating the single crystal silicon substratewithout conducting a high-temperature heat treatment. Moreover, thepresent inventors have found out that it is not indispensable to formp-n junction interfaces in parallel with a light receiving surface incase of using the thin-film single crystal silicon layer as the lightconversion layer, and it is also possible to form p-n junctioninterfaces in a direction perpendicular to the light receiving surfaceto establish a structure for extracting a photovoltaic power.Furthermore, the present inventors have conceived that such a thin-filmsolar cell is allowed to act as a so-called see-through type solar cellwhich can be seen through from one surface side toward the other surfaceside and which is also usable as a window material of a house, therebycompleting the present invention.

Although the embodiment of the present invention will be concretelydescribed, the present invention is not limited thereto.

FIG. 1 is a process diagram of an example of a method for producing asingle crystal silicon solar cell according to the present invention.

Firstly, there are prepared a single crystal silicon substrate 11 and atransparent insulator substrate 12 (stage “a”).

The single crystal silicon substrate is not limited to a particular one,and it is possible to adopt a single crystal silicon substrate which isobtained by slicing a single crystal exemplarily grown by a Czochralskimethod, and which is 100 to 300 mm in diameter, p-type or n-type inconductivity type, and about 0.1 to 20 Ω·cm in specific resistance, forexample.

Further, selected as the transparent insulator substrate is quartzglass, crystallized glass, borosilicate glass, soda-lime glass, or thelike. Although selectable glasses are not limited thereto, such glassmaterials are desirable in view of the fact that they are transparentand are each capable of alternatively acting as a window glass material.Further, in case of adopting a glass material made of general-purposesoda-lime glass as the transparent insulator substrate, it is possibleto adopt one having a surface formed with a silicon oxide coating, tinoxide coating (Nesa film), or the like by a dip coating method. Such acoating is desirable because it acts as a buffer film for preventingelution and diffusion of an alkali metal component in the soda-limeglass to the surface of the glass.

Next, at least one of hydrogen ions and rare gas ions is implanted intothe single crystal silicon substrate 11, to form an ion implanted layer14 therein (stage “b”).

For example, the temperature of the single crystal silicon substrate isbrought to 200 to 450° C., and at least one of hydrogen ions and raregas ions at a predetermined dosage is implanted into the single crystalsilicon substrate at such an implantation energy capable of forming anion implanted layer 14 at that depth from a surface 13 of the singlecrystal silicon substrate which corresponds to a desired thickness of asingle crystal silicon layer such as a depth of 0.1 to 5 μm or less. Inthis case, hydrogen ions are particularly desirable, since they arelight-weighted and thus can be implanted into a larger depth from theion implanting surface 13 by the same acceleration energy. The hydrogenions may be either positive or negative in charge, and may be hydrogengas ions in addition to hydrogen atom ions. Also in case of rare gasions, charge thereof may be either positive or negative.

Further, there can be obtained an effect for suppressing channeling ofimplanted ions, by previously forming an insulator film such as a thinsilicon oxide film at a surface of the single crystal silicon substrate,and by achieving ion implantation through the insulator film.

Next, the single crystal silicon substrate 11 is closely contacted withthe transparent insulator substrate 12 via a transparent adhesive 15,while using the ion implanting surface 13 as a bonding surface (stage“c”).

Desirably usable as the transparent adhesive is a resin having anexcellent visible light transmissivity, such as an acrylic resin,alicyclic acrylic resin, silicone resin, liquid crystal polymer,polycarbonate, and polyethylene terephthalate. Without limited thereto,the transparent adhesive to be used is to desirably have a transmittanceof visible light of 80% or more. Further, the single crystal siliconsubstrate and the transparent insulator substrate are closely contactedwith each other through such a transparent adhesive. At this time, theion implanting surface 13 of the single crystal silicon substrate isused as the bonding surface.

Concretely, there is firstly formed a transparent adhesive layer on atleast one of the single crystal silicon substrate and the transparentinsulator substrate, for example. Usable for formation of thetransparent adhesive layer is a coating method such as slit-die coatingand dip coating. Thereafter, the single crystal silicon substrate andthe transparent insulator substrate are closely contacted with eachother through the transparent adhesive layer.

Next, the transparent adhesive 15 is cured and matured into atransparent adhesive layer 16, to bond the single crystal siliconsubstrate 11 and the transparent insulator substrate 12 to each other(stage “d”).

The curing method of the transparent adhesive is not particularlylimited, and is appropriately selected in conformity to the usedmaterials. For example, it is possible to cure the transparent adhesiveto strongly bond the single crystal silicon substrate and thetransparent insulator substrate to each other, by a method of onceheating the transparent adhesive to about 250° C. to thereby soften itand then cooling it again, a method of volatilizing a solvent of theadhesive, or the like. Only, this curing treatment is to be conductedunder a temperature condition from a room temperature to about 250° C.,and no heat treatments are conducted at 300° C. or higher. This isbecause, when a high-temperature heat treatment at 300° C. or higher isconducted in a state that the single crystal silicon substrate 11 andthe transparent insulator substrate 12 are bonded to each other, thereis a possibility of occurrence of heat distortion, cracks, debonding,and the like, due to a difference between thermal expansion coefficientsof the substrates 11 and 12. In this way, avoidance of ahigh-temperature heat treatment at 300° C. or higher is also applicable,until completion of delaminative transference from the single crystalsilicon substrate 11 in the stage “e” to be described later.

Next, there is applied an impact to the ion implanted layer 14 tomechanically delaminate the single crystal silicon substrate 11 thereatto leave a single crystal silicon layer 17 (stage “e”)

In the present invention, since the mechanical delamination is conductedby applying an impact to the ion implanted layer, there is nopossibility of occurrence of heat distortion, cracks, debonding, and thelike due to heating. Although it is enough that a jet of fluid such asgas, liquid, or the like is continuously or intermittently blown ontothe joined wafer from the side thereof so as to apply an impact to theion implanted layer, the impacting method is not particularly limitedinsofar as capable of causing mechanical delamination by impact.

Note that it is desirable to conduct delamination of the single crystalsilicon substrate upon mechanical delamination thereof, by closelycontacting a first auxiliary substrate with the back surface of thetransparent insulator substrate and closely contacting a secondauxiliary substrate with the back surface of the single crystal siliconsubstrate. Conducting the mechanical delamination by using suchauxiliary substrates, prevents occurrence of small cracks due to warpageand crystal defects due to such cracks in the delaminatedly transferredsingle crystal silicon layer 17, thereby enabling prevention ofdegradation of a conversion efficiency of a solar cell. This methodexhibits a remarkable effect, in case that each substrate has a smallthickness such as about 1 mm or less. For example, when the transparentinsulator substrate is made of soda-lime glass and has a thickness of0.7 mm, delamination is conducted by adopting an auxiliary substratesimilarly made of soda-lime glass and by establishing a total thicknessof 1 mm or more for both substrates.

Further, it is possible to conduct a heat treatment after conducting thedelaminative transference from the single crystal silicon substrate, soas to heal ion implantation damages near the surface of the singlecrystal silicon layer 17. Since the delaminative transference from thesingle crystal silicon substrate 11 has been already completed at thistime to leave the thin-film single crystal silicon layer 17, cracks anddefects accompanying thereto are hardly caused in the single crystalsilicon layer even by conduction of a local heat treatment at 300° C. orhigher near the surface of the single crystal silicon layer. This isalso applicable to the following stages.

Next, there are formed a plurality of diffusion regions 22 of a secondconductivity type at the delaminated surface side of the single crystalsilicon layer 17, which conductivity type is different from a firstconductivity type of the single crystal silicon substrate prepared inthe stage “a”. At this time, the formation is conducted in a manner thata plurality of p-n junctions are formed at least in the plane direction(i.e., normal lines of p-n junction interfaces have at least a componentoriented in the plane direction of the single crystal silicon layer 17),and that the plurality of first conductivity-type regions 21 and theplurality of second conductivity-type regions 22 are present at thedelaminated surface of the single crystal silicon layer 17 (stage “f”).

When the single crystal silicon substrate 11 prepared in the stage “a”is a p-type single crystal silicon, the first conductivity type is ap-type, so that diffusion regions of an n-type as the secondconductivity type are formed. Contrary, in case of an n-type singlecrystal silicon, the first conductivity type is an n-type, so thatdiffusion regions of a p-type as the second conductivity type areformed. For example, it is possible to conduct the concrete method offorming the plurality of second conductivity type diffusion regions, asfollows. When the single crystal silicon substrate 11 prepared in thestage “a” is of p-type, element ions of phosphorus are implanted by anion implantation method into a plurality of regions (such as a pluralityof parallel line shaped regions) of the surface of the single crystalsilicon layer 17, and there is conducted an activating treatment fordonors at the implanted regions by performing: flash-lamp annealing;laser irradiation of ultraviolet light or deep ultraviolet light havinga higher absorption coefficient at the surface of the single crystalsilicon layer; or the like; thereby enabling formation of a plurality ofp-n junctions. At this time, it is desirable to appropriately adjust anion implantation amount, a diffusion time, an activation time, and thelike, in order to avoid that a plurality of n-type diffusion regions areoverlapped with one another into a single region. Further, such aformation of the plurality of p-n junctions may be conducted in amanner: to prepare a paste-like composite containing phosphorus forforming donors; to coat the composite onto a plurality of regions (suchas a plurality of parallel line shaped regions) of the surface of thesingle crystal silicon layer 17 such as by screen printing; and toconduct a diffusion treatment and an activating treatment for the coatedcomposite by, flash-lamp annealing, laser irradiation of ultravioletlight or deep ultraviolet light having a higher absorption coefficientat the surface of the single crystal silicon layer, an infrared furnace,or the like.

Note that the second conductivity-type regions 22 may be formed deeplyto reach the joining interface between the single crystal silicon layer17 and the transparent adhesive layer 16.

Further, it is possible to form high-concentration diffusion regions ofa first conductivity type among the plurality of second conductivitytype diffusion regions while forming the latter. For example, in case ofdiffusing phosphorus or the like into a plurality of regions of thep-type silicon substrate to bring them into a plurality of n-typediffusion regions, it is possible that an element such as boron forforming acceptors is subjected to a diffusion treatment and anactivating treatment at a plurality of regions among the plurality ofn-type diffusion regions in the same manner, thereby forming a pluralityof p⁺ regions.

Next, there are formed a plurality of first individual electrodes 23 onthe plurality of first conductivity-type regions 21 of the singlecrystal silicon layer 17, respectively, and a plurality of secondindividual electrodes 24 on the plurality of second conductivity-typeregions 22, respectively (stage “g”).

For example, the plurality of first individual electrodes 23 are formedon the plurality of first conductivity-type regions 21, respectively,and the plurality of second individual electrodes 24 are formed on theplurality of second conductivity-type regions 22 at the surface of thesingle crystal silicon layer 17, by adopting a metal or a transparentelectroconductive material and by using a vacuum deposition method or aconversion sputtering method. Further, it is possible to adopt variousknown methods including one to coat a paste-like composite containingmetal and the like for forming individual electrodes onto thepredetermined regions such as by printing, followed by curing based on aheat treatment.

Note that attention is to be paid at this time such that the firstindividual electrodes 23 are not joined to the second conductivity-typeregions 22 and the second individual electrodes 24 are not joined to thefirst conductivity-type regions 21, respectively.

Note that the diffusion region formation at the stage “f” and theindividual electrode formation at the stage “g” can be simultaneouslyconducted, as follows. Namely, it is possible to coat an electrodeformation composite containing a dopant material to be matured intodonors or acceptors onto the predetermined regions by printing or inkjetting, and to conduct a heat treatment to thereby cure and form aplurality of electrodes and diffuse the dopant simultaneously therewith.Also in this case, the heat treatment can be conducted by: flash-lampannealing; laser irradiation of ultraviolet light or deep ultravioletlight having a higher absorption coefficient at the surface of thesingle crystal silicon layer; an infrared furnace; or the like.

Meanwhile, in order to provide the solar cell according to the presentinvention as a see-through type which can be seen through from onesurface side toward the other surface side, it is desirable that theindividual electrode formation composite is coated at intervals of 10 μmor more, more preferably 100 μm or more. Since the single crystalsilicon layer 17 according to the present invention is free of crystalgrain boundaries such that mobilities of optically produced carriers andlifetimes thereof are the same as those in an ordinary single crystalsilicon substrate, it is allowed to cause intervals of the individualelectrode formation composite to be widened than those for apolycrystalline silicon thin-film and an amorphous silicon thin-film,which also contributes to improvement of the visible lighttransmissivity of the solar cell according to the present invention.

Next, there are formed a first collector electrode 25 for connecting theplurality of first individual electrodes 23 to one another and a secondcollector electrode 26 for connecting the plurality of second individualelectrodes 24 (stage “h”).

At this time, although the manner of connection is not particularlylimited, it is required that the first collector electrode 25 isprevented from contacting with the second conductivity-type regions 22and the second individual electrodes 24, and the second collectorelectrode 26 is prevented from contacting with the firstconductivity-type regions 21 and the first individual electrodes 23.

Forming the first collector electrode 25 and second collector electrode26 in this way allows for effective extraction of electrons and holescollected in the plurality of first individual electrodes 23 and theplurality of second individual electrodes 24, respectively.

It is further possible to additionally form a protective film or thelike made of silicon nitride or the like on the single crystal siliconlayer 17, after formation of the various electrodes.

The single crystal silicon solar cell produced by the stages “a” through“h” is a single crystal silicon solar cell 31, which is free ofoccurrence of heat distortion, debonding, cracks, and the like uponproduction, which is thin and has an excellent uniformity of filmthickness, which is excellent in crystallinity, and which has a singlecrystal silicon layer on a transparent insulator substrate.

Note that the remaining single crystal silicon substrate afterdelaminative transference of the single crystal silicon layer 17therefrom in the stage “e”, can be again utilized as a single crystalsilicon substrate 11, by conducting a treatment of polishing, smoothing,and removing the rough surface and the ion implanted layer afterdelamination, and by conducting an ion implantation treatmentrepeatedly. Since it is unnecessary in the method for producing a singlecrystal silicon solar cell of the present invention to heat the singlecrystal silicon substrate to a temperature of 300° C. or higherthroughout the ion implantation stage to the delamination stage, thereis no possibility that defects induced by oxygen are introduced into thesingle crystal silicon substrate. As such, it becomes possible toconduct delaminative transference as many as 100 or more times, in caseof firstly adopting a single crystal silicon substrate having athickness slightly less than 1 mm and setting the film thickness of asingle crystal silicon layer 17 to be 5 μm.

As schematically shown in FIG. 2, the single crystal silicon solar cell31 produced by such a production method is configured such that: thetransparent insulator substrate 12, the transparent adhesive layer 16,and the single crystal silicon layer 17 are successively laminated; thesingle crystal silicon layer 17 is formed with the plurality of firstconductivity-type regions 21 and the plurality of secondconductivity-type regions 22 at a surface (delaminated surface) sideopposite to the transparent adhesive layer 16 side; the plurality of p-njunctions are formed at least in the plane direction (i.e., normal linesof p-n junction interfaces have at least a component oriented in theplane direction of the single crystal silicon layer 17); the pluralityof first conductivity-type regions 21 of the single crystal siliconlayer 17 are formed thereon with the plurality of first individualelectrodes 23, respectively; the plurality of second conductivity-typeregions 22 are formed thereon with the plurality of second individualelectrodes 24, respectively; and the first collector electrode 25 isformed to connect the plurality of first individual electrodes 23 to oneanother, and the second collector electrode 26 is formed to connect theplurality of second individual electrodes 24 to one another.

When the single crystal silicon layer 17 has a thickness between 0.1 μmand 5 μm, it is possible to obtain a practical efficiency as a thin-filmsingle crystal silicon solar cell and to sufficiently save an amount ofsilicon material to be used. Further, the single crystal silicon solarcell having such a thickness of single crystal silicon layer isassuredly capable of transmitting part of visible light therethrough andthus becoming transparent.

Further, the single crystal silicon solar cell 31 according to thepresent invention can be seen through from one surface side toward theother surface side, and it is possible in this case to adopt either ofthe transparent insulator substrate 12 side or the side formed with thevarious electrodes, as a light receiving surface.

Example

Prepared as a single crystal silicon substrate 11 was a single crystalsilicon substrate of a p-type, having a diameter of 200 mm (8 inches),one surface which was mirror-polished, a crystal face (100), and aspecific resistance of 15 Ω·cm. Further prepared as a transparentinsulator substrate 12 was a quartz glass substrate having a diameter of200 mm (8 inches) and a thickness of 2.5 mm (stage “a”).

Next, hydrogen cations were implanted into the single crystal siliconsubstrate 11 under a condition of an acceleration voltage of 350 keV anda dosage of 1.0×10¹⁷/cm² (stage “b”). This resulted in a depth of an ionimplanted layer 14 at about 3 μm from an ion implanting surface 13.

Subsequently, there were used alkyltrialkoxysilane and tetraalkoxysilanetogether with hydrochloric acid as a catalyst, to obtain a hydrolyticpolycondensate. This was dissolved in a solvent of isopropyl alcohol, toprepare a transparent adhesive (silicone resin). Through thistransparent adhesive 15, the single crystal silicon 11 and the quartzglass substrate 12 were closely contacted with each other (stage “c”).

The thus bonded substrates were subjected to a heat treatment at 250° C.for 2 hours, and cooled down to a room temperature to thereby cure thetransparent adhesive 15 as a transparent adhesive layer 16, therebystrongly bonding the single crystal silicon 11 and the quartz glasssubstrate 12 to each other (stage “d”).

Next, there was blown a high pressure nitrogen gas onto the vicinity ofthe joining interface, followed by conduction of mechanical delaminationfor delaminating the single crystal silicon substrate in a manner toinitiate the delamination from the blown surface (stage “e”). At thistime, the delamination was conducted after suckingly attaching auxiliarysubstrates from the back to the single crystal silicon substrate andquartz glass substrate, respectively. Further, irradiation was conductedonto the delaminatedly transferred single crystal silicon by flash-lampannealing under a condition that the surface of the single crystalsilicon was momentarily brought to a temperature of 700° C. or higher,thereby healing hydrogen implantation damages.

Formed on the surface of the single crystal silicon layer 17 was apattern of line widths of 50 μm at intervals of 1 mm by screen printing,made of a diffusion paste containing ethyl cellosolve includingphosphosilicate glass as a thickener. Irradiation was conducted theretoby a flash lamp such that the surface was momentarily heated to 600° C.or higher, thereby forming a plurality of n-type diffusion regions 22each at a joining depth of about 0.2 μm (stage “f”). This resulted inalternating presence of p-type regions 21 and n-type regions 22 at thesurface of the single crystal silicon layer 17, thereby forming aplurality of p-n junctions in the plane direction.

This diffusion paste was subjected to removal and cleaning byhydrofluoric acid, acetone, and isopropyl alcohol, followed by formationof first individual electrodes 23 on the plurality of p-type region 21and second individual electrodes 24 on the plurality of n-type regions22, respectively, by vacuum deposition and patterning while adoptingsilver as an electrode material (stage “g”).

Subsequently, there were formed a first collector electrode 25 forconnecting the plurality of first individual electrodes 23 to oneanother and a second collector electrode 26 for connecting the pluralityof second individual electrodes 24 to one another, by vacuum depositionwith metal masks, respectively, while adopting silver as electrodematerials (stage “h”). There was then formed a protective coating ofsilicon nitride over the surface by reactive sputtering, except forportions of pickup electrodes.

In this way, there was produced a thin-film single crystal silicon solarcell 31 as shown in FIG. 2, in such a configuration that: thetransparent insulator substrate, the transparent adhesive layer, and thesingle crystal silicon layer are successively laminated; the singlecrystal silicon layer is formed with the plurality of p-type regions andthe plurality of n-type regions at the surface side opposite to thetransparent adhesive layer side; the plurality of p-n junctions areformed at least in the plane direction; the plurality of p-type regionsof the single crystal silicon layer are formed thereon with theplurality of first individual electrodes, respectively; the plurality ofn-type regions are formed thereon with the plurality of secondindividual electrodes, respectively; and the first collector electrodeis formed to connect the plurality of first individual electrodes to oneanother, and the second collector electrode is formed to connect theplurality of second individual electrodes to one another.

Irradiated to the thus produced single crystal silicon solar cell was alight of 100 mW/cm² under AM1.5 conditions by a solar simulator, therebymeasuring a conversion efficiency. The conversion efficiency was 8.4%,and timewise change was not observed.

Further, it was possible to see a situation in a room by lookingthereinto through the solar cell while allowing outside light to enterthe room therethrough during a fine day.

Note that the present invention is not limited to the above embodiment.The embodiment is merely exemplary, and whatever has substantially thesame configuration and exhibit the same functions and effects as thetechnical concept recited in the appended claims of the presentapplication shall be embraced within the technical concept of thepresent invention.

1. A method for producing a single crystal silicon solar cell, the solarcell including a transparent insulator substrate and a single crystalsilicon layer arranged on the transparent insulator substrate and actingas a light conversion layer, the method comprising at least the stepsof: preparing the transparent insulator substrate and a single crystalsilicon substrate having a first conductivity type; implanting at leastone of hydrogen ions and rare gas ions into the single crystal siliconsubstrate through an ion implanting surface thereof to form an ionimplanted layer in the single crystal silicon substrate; closelycontacting the single crystal silicon substrate and the transparentinsulator substrate with each other via a transparent adhesive whileusing the ion implanting surface as a bonding surface; curing andmaturing the transparent adhesive into a transparent adhesive layer, tobond the single crystal silicon substrate and the transparent insulatorsubstrate to each other; applying an impact to the ion implanted layerto mechanically delaminate the single crystal silicon substrate thereatto leave a single crystal silicon layer; forming a plurality ofdiffusion regions having a second conductivity type at the delaminatedsurface side of the single crystal silicon layer, which conductivitytype is different from the first conductivity type, in a manner that aplurality of p-n junctions are formed at least in the plane direction,and that the plurality of first conductivity-type regions and theplurality of second conductivity-type regions are present at thedelaminated surface of the single crystal silicon layer; forming aplurality of first individual electrodes on the plurality of firstconductivity-type regions of the single crystal silicon layer,respectively, and a plurality of second individual electrodes on theplurality of second conductivity-type regions, respectively; and forminga first collector electrode for connecting the plurality of firstindividual electrodes to one another and a second collector electrodefor connecting the plurality of second individual electrodes to oneanother.
 2. The method for producing a single crystal silicon solar cellaccording to claim 1, wherein the transparent insulator substrate ismade of any one of quartz glass, crystallized glass, borosilicate glass,and soda-lime glass.
 3. The method for producing a single crystalsilicon solar cell according to claim 1, wherein the transparentadhesive is configured to contain at least one of a silicone resin, anacrylic resin, an alicyclic acrylic resin, a liquid crystal polymer, apolycarbonate, and a polyethylene terephthalate.
 4. The method forproducing a single crystal silicon solar cell according to claim 2,wherein the transparent adhesive is configured to contain at least oneof a silicone resin, an acrylic resin, an alicyclic acrylic resin, aliquid crystal polymer, a polycarbonate, and a polyethyleneterephthalate.
 5. The method for producing a single crystal siliconsolar cell according to claim 1, wherein the ion implantation isconducted at a depth between 0.1 μm inclusive and 5 μm inclusive fromthe ion implanting surface.
 6. The method for producing a single crystalsilicon solar cell according to claim 2, wherein the ion implantation isconducted at a depth between 0.1 μm inclusive and 5 μm inclusive fromthe ion implanting surface.
 7. The method for producing a single crystalsilicon solar cell according to claim 3, wherein the ion implantation isconducted at a depth between 0.1 μm inclusive and 5 μm inclusive fromthe ion implanting surface.
 8. The method for producing a single crystalsilicon solar cell according to claim 4, wherein the ion implantation isconducted at a depth between 0.1 μm inclusive and 5 μm inclusive fromthe ion implanting surface.
 9. A single crystal silicon solar cellproduced by the method for producing a single crystal silicon solar cellaccording to claim
 1. 10. A single crystal silicon solar cellcomprising: at least, a transparent insulator substrate, a transparentadhesive layer, and a single crystal silicon layer, which aresuccessively laminated; a plurality of first conductivity-type regionsand a plurality of second conductivity-type regions formed in the singlecrystal silicon layer at a surface side thereof opposite to thetransparent adhesive layer side; a plurality of p-n junctions formed atleast in the plane direction of the single crystal silicon layer; aplurality of first individual electrodes formed on the plurality offirst conductivity-type regions of the single crystal silicon layer,respectively, and a plurality of second individual electrodes formed onthe plurality of second conductivity-type regions of the single crystalsilicon layer, respectively; and a first collector electrode forconnecting the plurality of first individual electrodes to one another,and a second collector electrode for connecting the plurality of secondindividual electrodes to one another.
 11. The single crystal siliconsolar cell according to claim 10, wherein the transparent insulatorsubstrate is made of any one of quartz glass, crystallized glass,borosilicate glass, and soda-lime glass.
 12. The single crystal siliconsolar cell according to claim 10, wherein the transparent adhesive layeris configured to contain at least one of a silicone resin, an acrylicresin, an alicyclic acrylic resin, a liquid crystal polymer, apolycarbonate, and a polyethylene terephthalate.
 13. The single crystalsilicon solar cell according to claim 11, wherein the transparentadhesive layer is configured to contain at least one of a siliconeresin, an acrylic resin, an alicyclic acrylic resin, a liquid crystalpolymer, a polycarbonate, and a polyethylene terephthalate.
 14. Thesingle crystal silicon solar cell according to claim 10, wherein thesingle crystal silicon layer has a thickness between 0.1 μm inclusiveand 5 μm inclusive.
 15. The single crystal silicon solar cell accordingto claim 11, wherein the single crystal silicon layer has a thicknessbetween 0.1 μm inclusive and 5 μm inclusive.
 16. The single crystalsilicon solar cell according to claim 12, wherein the single crystalsilicon layer has a thickness between 0.1 μm inclusive and 5 μminclusive.
 17. The single crystal silicon solar cell according to claim13, wherein the single crystal silicon layer has a thickness between 0.1μM inclusive and 5 μm inclusive.
 18. The single crystal silicon solarcell according to claim 9, wherein the single crystal silicon solar cellcan be seen through from one surface side toward the other surface side.19. The single crystal silicon solar cell according to claim 10, whereinthe single crystal silicon solar cell can be seen through from onesurface side toward the other surface side.
 20. The single crystalsilicon solar cell according to claim 11, wherein the single crystalsilicon solar cell can be seen through from one surface side toward theother surface side.
 21. The single crystal silicon solar cell accordingto claim 12, wherein the single crystal silicon solar cell can be seenthrough from one surface side toward the other surface side.
 22. Thesingle crystal silicon solar cell according to claim 13, wherein thesingle crystal silicon solar cell can be seen through from one surfaceside toward the other surface side.
 23. The single crystal silicon solarcell according to claim 14, wherein the single crystal silicon solarcell can be seen through from one surface side toward the other surfaceside.
 24. The single crystal silicon solar cell according to claim 15,wherein the single crystal silicon solar cell can be seen through fromone surface side toward the other surface side.
 25. The single crystalsilicon solar cell according to claim 16, wherein the single crystalsilicon solar cell can be seen through from one surface side toward theother surface side.
 26. The single crystal silicon solar cell accordingto claim 17, wherein the single crystal silicon solar cell can be seenthrough from one surface side toward the other surface side.
 27. Thesingle crystal silicon solar cell according to claim 18, wherein thesingle crystal silicon solar cell can be seen through from one surfaceside toward the other surface side.